The editor option provided very little value, but occupied a considerable space in Preferences.
I think what you need is not editor, but edit. May I ask why you have to edit known hosts frequently? Personally, I rarely touch known hosts file after accepted the host keys deliberately.
I am currently migrating 100's of cPanel servers to new infrastructure and when I go to connect to the new server once migrated (to the same IP as it was originally) I encounter this.
It's a shame it was removed as it was very handy and was only an extra tab but thanks for the explanation I will just have to edit the file manually.